The present invention relates to actuators and, more particularly, to adjustment mechanisms usable as height adjusters in a variety of articles including furniture.
Various forms of telescoping actuators are presently available for supporting and/or adjusting the position of two different elements. In furniture applications, such actuators are used with chairs, tables, work surfaces and the like. Currently available actuators include hydraulic, pneumatic, pressurized gas or mechanical devices.
In the seating area, actuators or support columns are used to set the vertical height of the seat and adjust the seating to the user and/or the task. Examples of mechanical actuators may be found in U.S. Pat. No. 4,709,894 entitled SLIP CONNECTOR FOR WEIGHT ACTUATED HEIGHTADJUSTERS, which issued on Dec. 1, 1987, to Knoblock et al. and U.S. Pat. No. 5,234,187 entitled CHAIR HEIGHT ADJUSTMENT MECHANISM, which issued on Oct. 10, 1993, to Teppo et al. The adjuster of U.S. Pat. No. 4,709,894 is functional when the seat is unoccupied. The actuator disengages when the seat is occupied to permit the seat to swivel on the base without an effect on the seat height. The adjustment mechanism of U.S. Pat. No. 5,234,187 includes telescoping outer, intermediate and inner tubes and a drive which extends the telescoping tubes to adjust the height of the load. In one form, the drive includes a flexible, substantially nonelastic tape. A piston/cylinder gas spring or actuator is also included to extend the tubes.
Examples of pneumatic adjustment mechanisms and hydraulic or combination pneumatic/hydraulic adjustment mechanisms may be found in U.S. Pat. No. 3,381,926 entitled ADJUSTABLE STOOL, which issued on May 7, 1968, to Fritz et al; U.S. Pat. No. 4,139,175 entitled HEIGHT-ADJUSTABLE CHAIR OR TABLE PEDESTAL, which issued on Feb. 13, 1979, to Bauer; U.S. Pat. No. 4,445,671 entitled GAS SPRING INCLUDING HYDRAULIC LOCKING MEANS, which issued on May 1, 1984, to Reuschenbach et al; and U.S. Pat. No. 4,997,150 entitled ADJUSTABLE OLEOPNEUMATIC SUPPORT, which issued on Mar. 5, 1991, to Mardollo.
Extendable adjustment mechanisms, especially those used in the furniture industry, need to provide for varying loads, stability, shock absorbency, fine height adjustment, controlled movement, appropriate ranges of travel, accommodate swivel action and be reliable with reasonable service lives. Achieving these desirable ends results in compromises in presently existing systems, undue complexity or high costs.
Prior pneumatic or gas actuators operate at relatively high pressures. The high gas pressures and operating characteristics result in leakage or seal failure problems and complexity. Operational problems, including adjustment overshoot, are experienced. Extension or retraction rates are not controllable. Gas actuators require stops at the end of travel to provide protection to the mechanism and avoid a hard landing or shock to the user. In the seating area, it is also desirable to provide controlled shock absorbency. The shock-absorbent characteristics of pneumatic or gas actuators are poor. The damping characteristics of the gas is uncontrollable, which results in overshoot and bounce. Hydraulic systems may employ a gas spring or a mechanical spring for shock absorbency. Mechanical springs suffer from overshoot and bounce. In addition, the spring can bottom-out, resulting in a hard stop or excessive shock to the user. Lastly, it is desirable to provide a sufficiently broad range of travel. For example, current standards suggest that a chair should be adjustable from 16-inches to 20.5-inches above the floor. Such a range is not always possible with existing technology.
A need exists for an improved actuator which will provide a long-term service life, increased reliability and improved operational characteristics at reduced cost from those presently experienced.